This invention relates to vulcanizable semi-conductive compositions which provide strippable semi-conductive insulation shielding compositions for insulated electrical conductors.
The construction of insulated electrical conductors, i.e. wires and cables, designed for medium to high voltage applications is well known in the art and commonly comprises a core conductor which comprises one or more strands of a conducting metal or alloy such as copper or aluminum, a layer of semi-conductive conductor shielding, a layer of insulation, such as crosslinked polyethylene, and a layer of semi-conductive insulation shielding overlying said insulation. A plurality of neutral wires which are usually made of copper or aluminum may be embedded in or wrapped around the layer of semi-conducting insulation shielding, if desired, in the form of a concentric ring around the insulated cable.
The formation of crosslinking bonds between the insulation and shielding makes subsequent separation of the two layers (insulation and semi-conductive shielding) such as occurs in making splices or terminal connections, very difficult and time consuming. Such a strong bond also makes the semi-conductive layer prone to leave carbon residue on the insulation even when it is finally peeled off. Accordingly, a strippable semi-conductive shielding which can be easily and cleanly stripped from the insulation of an insulated conductor is therefore very desirable in this art.
It has now been discovered that strippable semi-conductive insulation shielding compositions can be prepared from the vulcanizable semi-conductive insulation shielding compositions of this invention which contain both an ethylene copolymer and butadiene-acrylonitrile copolymer as described more fully below.
Thus, it is an object of this invention to provide a vulcanizable semi-conductive insulation shielding composition which is particularly useful for providing a strippable shielding for insulated electrical conductors, e.g. wires and cables, that contain, as the primary insulation, a crosslinked polyolefin. Another object of this invention is to provide an article of manufacture comprising the crosslinked product of said vulcanizable semi-conductive insulation shielding composition of this invention bonded directly to a crosslinked polyolefin substrate. Yet another object of this invention is to provide an article of manufacture as defined above wherein said crosslinked polyolefin is the primary insulation of an insulated electrical conductor, thus providing insulated electrical conductors, e.g. wires and cables, comprising, as the primary insulation, a crosslinked polyolefin, and as the material for said insulation an easily strippable crosslinked semi-conductive shielding composition. Other objects and advantages of this invention will become readily apparent from the following description and appended claims.